What is called a rear-wheel lift phenomenon (hereinafter referred to as a rear-wheel lift) that the rear wheel lifts up at the time of sudden braking sometimes occurs in vehicles with bar handle. A vehicle running in a rear-wheel lift state is unstable in vehicle behavior. Japanese Patent No. 5014159 discloses a technique for suppressing a rear-wheel lift.
In the technique disclosed in Japanese Patent No. 5014159, if deceleration (negative value) of a vehicle body that is calculated on the basis of vehicle body speeds detected by wheel speed sensors for the front wheel and the rear wheel becomes smaller than a prescribed value (negative value) during braking, the pressure of a front wheel cylinder is lowered and kept at a lowered pressure (paragraphs 0024 and 0028 and FIGS. 3(B) and 4 of Japanese Patent No. 5014159).
What is called a wheelie state in which the front wheel lifts up during acceleration occurs in vehicles with bar handle. A vehicle running in a wheelie state is also unstable in vehicle behavior.
In Japanese Patent No. 5014159, the probability of occurrence of a rear-wheel lift is judged on the basis of vehicle body acceleration that is calculated from detection values (a front wheel speed and a rear wheel speed) of the wheel speed sensors for the front wheel and the rear wheel.
However, if the probability of occurrence of a rear-wheel lift is judged only on the basis of vehicle body acceleration that is calculated from detection values (a front wheel speed and a rear wheel speed) of the wheel speed sensors for the front wheel and the rear wheel, and a control of lowering the fluid pressure of a wheel brake is started, the fluid pressure control is not always started with proper timing.